This experiment mainly learned some commonly used system calls.
Lab 1: Unix utilities
Boot xv6 (easy)
git clone, switch branches, qemu. Just proceed as required.
$ git clone git://g.csail.mit.edu/xv6-labs-2020 $ cd xv6-labs-2020 $ git checkout util $ makeqemu
sleep (easy)
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
int main(int argc,char *argv[])
{
if(argc < 2)
{
fprintf(2,"please enter a number!");
exit(1);
}else{
int n = atoi(argv[1]);
sleep(n);
exit(0);
}
}
Add sleep to the build target in the Makefile.
UPROGS=\ $U/_cat\ $U/_echo\ $U/_forktest\ $U/_grep\ $U/_init\ $U/_kill\ $U/_ln\ $U/_ls\ $U/_mkdir\ $U/_rm\ $U/_sh\ $U/_stressfs\ $U/_usertests\ $U/_grind\ $U/_wc\ $U/_zombie\ $U/_sleep\ . # here !!!
pingpong (easy)
For pipe problems, use fork() to copy this process to create a child process, and then use pipes to communicate with each other.
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
int main(int argc,char *argv[])
{
int pp2c[2],pp2p[2];
pipe(pp2c);
pipe(pp2p);
int n = fork();
if(n != 0 ){
write(pp2c[1],"a",1);
char buff;
read(pp2p[0], & amp;buff,1);
printf("%d: received pong\
",n);
}else{
char buff;
read(pp2c[0], & amp;buff,1);
printf("%d: received ping\
",n);
write(pp2p[1], & amp;buff,1);
}
exit(0);
}
primes (moderate) / (hard)
Observe the picture below to understand, and use fork to implement the function of prime number sieve.
// primes.c
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
void sieve(int pleft[2]){<!-- -->
int p ;
read(pleft[0] , & amp;p,sizeof(p));
if(p == -1){<!-- -->
exit(0);
}
printf("prime %d\
", p);
int pright[2];
pipe(pright);
if(fork() == 0){<!-- -->
// child process
close(pright[1]);
close(pleft[0]);
sieve(pright);
}else{<!-- -->
close(pright[0]);
int buff;
while(read(pleft[0] , & amp;buff,sizeof(buff)) & amp; & amp; buff != -1){<!-- -->
if(buff %p != 0 ){<!-- -->
write(pright[1] , & amp;buff,sizeof(buff));
}
}
buff = -1;
write(pright[1] , & amp;buff,sizeof(buff));
wait(0);
exit(0);
}
}
int main(int argc,char* argv[]){<!-- -->
int inputpipe[2];
pipe(inputpipe);
if(fork() == 0){<!-- -->
// child process
close(inputpipe[1]);
sieve(inputpipe);
exit(0);
}else{<!-- -->
close(inputpipe[0]);
int i;
for( i = 2 ; i <=35;i + + ){<!-- -->
write(inputpipe[1] , & amp;i,sizeof(i) );
}
i =-1;
write(inputpipe[1] , & amp;i,sizeof(i) );
}
wait(0);
exit(0);
}
find (moderate)
Based on the transformation of ls.c
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
#include "kernel/fs.h"
void find(char *path,char *target)
{<!-- -->
char buf[512], *p;
int fd;
struct dirent de;
struct stat st;
if((fd = open(path, 0)) < 0){<!-- -->
fprintf(2, "ls: cannot open %s\
", path);
return;
}
if(fstat(fd, & amp;st) < 0){<!-- -->
fprintf(2, "ls: cannot stat %s\
", path);
close(fd);
return;
}
switch(st.type){<!-- -->
case T_FILE:
if(strcmp(path + strlen(path) - strlen(target) ,target) == 0)
printf("%s\
", path);
break;
case T_DIR:
if(strlen(path) + 1 + DIRSIZ + 1 > sizeof buf){<!-- -->
printf("find: path too long\
");
break;
}
strcpy(buf, path);
p = buf + strlen(buf);
*p + + = '/';
while(read(fd, & amp;de, sizeof(de)) == sizeof(de)){<!-- -->
if(de.inum == 0|| strcmp(de.name, ".")==0 || strcmp(de.name, ".." )==0 )
continue;
memmove(p, de.name, DIRSIZ);//It will be overwritten every time it loops
p[DIRSIZ] = 0;
if(stat(buf, & amp;st) < 0){<!-- -->
printf("find: cannot stat %s\
", buf);
continue;
}
// printf(buf);
// printf("\
");
find(buf, target); // Recursive search
\t\t
}
break;
}
close(fd);
}
int main(int argc, char *argv[])
{<!-- -->
if(argc < 3){<!-- -->
exit(0);
}
char target[512];
target[0] = '/'; // Add / at the beginning of the file name to be searched for
strcpy(target + 1, argv[2]);
find(argv[1], target);
exit(0);
}
xargs (moderate)
Introduction to xargs
Overall idea:
- Save the parameters passed in by the xargs command to an array of pointers, with each pointer pointing to a parameter;
- Parse the input parameters. If ‘ ‘ or \
is encountered, save the parameters to the pointer array. Use exec to run each time a line is read. - The last line is judged and run separately, in case the last line does not have a newline character
// xargs.c
#include "kernel/types.h"
#include "kernel/stat.h"
#include "user/user.h"
#include "kernel/fs.h"
void run(char *program, char ** args)
{<!-- -->
if(fork() == 0 ){<!-- -->
exec(program,args);
exit(0);
}
return ;
}
int main(int argc,char* argv[]){<!-- -->
char buf[2048]; // Memory pool used when reading
char *p = buf, *last_p = buf; // End and start pointers of the current parameter
char *argsbuf[128]; //All parameter list, string pointer array, including parameters passed in by argv and parameters read in by stdin
char **args = argsbuf; // Point to the first parameter in argsbuf read from stdin
for(int i=1;i<argc;i + + ) {<!-- -->
//Add the parameters provided by argv to the final parameter list
*args = argv[i];
args + + ;
}
char **pa = args;
while(read(0,p,1) != 0 ){<!-- -->
if(*p == ' ' || *p == '\
'){<!-- -->
*p = '\0';
*(pa + + ) = last_p;
last_p = p + 1;
if(*p == '\
'){<!-- -->
*pa = 0;
run(argv[1],argsbuf);
pa = args;
}
}
p + + ;
}
if(pa != args) {<!-- --> // If the last line is not a blank line
//Finish the last parameter
*p = '\0';
*(pa + + ) = last_p;
// End the last line
*pa = 0; // Use null at the end of the parameter list to identify the end of the list
//Execute the last line of instructions
run(argv[1], argsbuf);
}
while(wait(0) != -1) {<!-- -->};
exit(0);
}